'\" et
.TH MKTIME "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
mktime
\(em convert broken-down time into time since the Epoch
.SH SYNOPSIS
.LP
.nf
#include <time.h>
.P
time_t mktime(struct tm *\fItimeptr\fP);
.fi
.SH DESCRIPTION
The functionality described on this reference page is aligned with the
ISO\ C standard. Any conflict between the requirements described here and the
ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
.P
The
\fImktime\fR()
function shall convert the broken-down time, expressed as local time,
in the structure pointed to by
.IR timeptr ,
into a time since the Epoch value with the same encoding as that of the
values returned by
\fItime\fR().
The original values of the
.IR tm_wday
and
.IR tm_yday
components of the structure shall be ignored, and the original values
of the other components shall not be restricted to the ranges
described in
.IR <time.h> .
.P
A positive or 0 value for
.IR tm_isdst
shall cause
\fImktime\fR()
to presume initially that Daylight Savings Time, respectively, is or is
not in effect for the specified time. A negative value for
.IR tm_isdst
shall cause
\fImktime\fR()
to attempt to determine whether Daylight Savings Time is in effect for
the specified time.
.P
Local timezone information shall be set as though
\fImktime\fR()
called
\fItzset\fR().
.P
The relationship between the
.BR tm
structure (defined in the
.IR <time.h> 
header) and the time in seconds since the Epoch is that the result
shall be as specified in the expression given in the definition of
seconds since the Epoch (see the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 4.16" ", " "Seconds Since the Epoch")
corrected for timezone and any seasonal time adjustments, where the
names other than
.IR tm_yday
in the structure and in the expression correspond, and the
.IR tm_yday
value used in the expression is the day of the year from 0 to 365
inclusive, calculated from the other
.BR tm
structure members specified in
.IR <time.h> 
(excluding
.IR tm_wday ).
.P
Upon successful completion, the values of the
.IR tm_wday
and
.IR tm_yday
components of the structure shall be set appropriately, and the other
components shall be set to represent the specified time since the Epoch,
but with their values forced to the ranges indicated in the
.IR <time.h> 
entry; the final value of
.IR tm_mday
shall not be set until
.IR tm_mon
and
.IR tm_year
are determined.
.SH "RETURN VALUE"
The
\fImktime\fR()
function shall return the specified time since the Epoch encoded as
a value of type
.BR time_t .
If the time since the Epoch cannot be represented, the function shall
return the value (\fBtime_t\fP)\-1
and set
.IR errno
to indicate the error.
.SH ERRORS
The
\fImktime\fR()
function shall fail if:
.TP
.BR EOVERFLOW
The result cannot be represented.
.LP
.IR "The following sections are informative."
.SH "EXAMPLES"
What day of the week is July 4, 2001?
.sp
.RS 4
.nf

#include <stdio.h>
#include <time.h>
.P
struct tm time_str;
.P
char daybuf[20];
.P
int main(void)
{
    time_str.tm_year = 2001 \(em 1900;
    time_str.tm_mon = 7 \(em 1;
    time_str.tm_mday = 4;
    time_str.tm_hour = 0;
    time_str.tm_min = 0;
    time_str.tm_sec = 1;
    time_str.tm_isdst = -1;
    if (mktime(&time_str) == -1)
        (void)puts("-unknown-");
    else {
        (void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
        (void)puts(daybuf);
    }
    return 0;
}
.fi
.P
.RE
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIasctime\fR\^(\|)",
.IR "\fIclock\fR\^(\|)",
.IR "\fIctime\fR\^(\|)",
.IR "\fIdifftime\fR\^(\|)",
.IR "\fIgmtime\fR\^(\|)",
.IR "\fIlocaltime\fR\^(\|)",
.IR "\fIstrftime\fR\^(\|)",
.IR "\fIstrptime\fR\^(\|)",
.IR "\fItime\fR\^(\|)",
.IR "\fItzset\fR\^(\|)",
.IR "\fIutime\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 4.16" ", " "Seconds Since the Epoch",
.IR "\fB<time.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
